As the world's supply of crude oil becomes heavier and contains higher sulfur levels, there is a challenge is to meet the growing demand for light, high-quality, low-sulfur transportation fuels. The upgrading of heavy hydrocarbon feedstocks may help to meet this demand. Several processes are useful for upgrading heavy hydrocarbon feedstocks. One such process is known as slurry phase hydrocracking. Slurry-phase hydrocracking converts any hydrogen and carbon containing feedstock derived from mineral oils, synthetic oils, coal, biological processes, and the like, hydrocarbon residues, such as vacuum residue (VR), atmospheric residue (AR), de-asphalted bottoms, coal tar, and the like, in the presence of hydrogen under high temperatures and high pressures, for example, from about 750° F. (400° C.) up to about 930° F. (500° C.), and from about 1450 psig (10,000 kPa) up to about 4000 psig (27,500 kPa), or higher. To prevent excessive coking during the reaction, finely powdered additive particles made from carbon, iron salts, or other materials, may be added to the liquid feed. Inside the reactor, the liquid/powder mixture ideally behaves as a single homogenous phase due to the small size of the additive particles. In practice, the reactor may be operated as an up-flow bubble column reactor or as a circulating ebulated bed reactor and the like with three phases due to the hydrogen make up and light reaction products contributing to a gas phase, and larger additive particles contributing to a solid phase, and the smaller additive particles, feedstock and heavier reaction products contributing to the liquid phase, with the combination of additive and liquid comprising the slurry. In slurry phase hydrocracking, feedstock conversion may exceed 90% into valuable converted products, and even more than 95% when a vacuum residue is the feedstock.
One example of slurry phase hydrocracking is known as Veba Combi-Cracking™ (VCC™) technology. This technology typically operates in a once through mode where a proprietary particulate additive is added to a heavy feedstock, such as vacuum residue (VR), to form a slurry feed. The slurry feed is charged with hydrogen and heated to reactive temperatures to crack the vacuum residue into lighter products. The vaporized conversion products may or may not be further hydrotreated and/or hydrocracked in a second stage fixed bed catalyst reactor. It produces a wide range of distillate products including vacuum gas oil, middle distillate (such as diesel and kerosene), naphtha and light gas.
While the slurry phase hydrocracking is known for treating heavy fractions obtained from distilled crude oil, many refineries utilize other standalone processing units to convert middle fractions of crude oil into more valuable diesel and gasoline products. For example, heavy vacuum gas oil may be sent to a standalone hydrocracker to produce hydrocracked diesel, kerosene and gasoline. Vacuum gas oil and heavy atmospheric distillate may be sent to a standalone fluid catalytic cracker (FCC) to produce FCC gasoline. The mid-distillates (diesel and kerosene) obtained from an atmospheric distillation unit may be finished with a hydrotreater unit to obtained finished diesel or jet fuel. Naphtha fractions may be introduced into a hydrotreater unit before being sent to a catalytic reformer unit or isomeration unit to obtain reformate or isomerate useful for blending in a gasoline pool.
Despite the various processes and alternatives available for upgrading heavy hydrocarbons and lighter crude oil fractions, there is still a need for improving the existing processes to benefit the economics, efficiency and effectiveness of the unit operations. Likewise, in designing new grass root refineries, there are opportunities to develop simpler flow schemes with fewer standalone process units while still maintaining a full upgraded product slate, thereby significantly reducing operating complexity and capital requirements.